Known hose pumps of this type differ essentially in the manner in which the hose is raised again in the intake area behind a squeezing member which is moved along the hose in order to squeeze the hose.
For example, hose pumps are known which have an elastic hose which has a relatively high natural restoring force. The restoring force desired in each case then depends on the desired suction height of the pump.
In another known type of hose pump, the restoring force for the hose is generated by a negative pressure in the pump interior. Several possibilities for generating and maintaining the necessary negative pressure in the interior of the hose pump are known from German patent 37 03 124. In accordance with a first embodiment, the necessary negative pressure at the suction side for restoring the squeezed hose is generated by a separating device which consists of a sealing part and a separating part, wherein the sealing part constitutes an elastic sealing member which is connected to the circumferential wall of the housing in the short region between the intake connection and the pressure connection and which sealingly rests in this region against the separating part, the front wall, the rear wall and the circumferential wall, while the separating part is constructed as a sealing member which is guided around the rotor with the squeezing members and acts sealingly relative to the front wall and the rear wall. A separating device of this type generates in the pump the negative pressure on the suction side of such a magnitude which corresponds to the suction height required at a given time. The same effect is achieved in accordance with another embodiment by filling all free spaces in the interior of the pump with a liquid. Thus, in the filled state, when the squeezing member is moved ahead on the hose by a certain distance and squeezes a new portion of the hose, the previously squeezed piece of hose cannot remain squeezed because this would create a hollow space in the liquid filled into the pump, which is impossible. Accordingly, the effect of the liquid creates a negative pressure which immediately raises each squeezed piece of hose as soon as the squeezing member moves ahead. As a result, the hose is raised by means of negative pressure. This makes it possible to achieve very high rates of rotation and, thus, a high delivery of the pump. The negative pressure generated when the squeezing member is moved ahead corresponds also in this embodiment exactly to the negative pressure in the hose on the suction side. Accordingly, the suction height is automatically adjusted also in this pump.
Compared to hose pumps having an elastic hose, hose pumps in which the hose is restored by a negative pressure are of more complicated construction which is understandable because of the necessary vacuum-tight construction. Thus, obtaining the negative pressure when mounting the separating device depends on the vacuum-tight connection of the components which move relative to each other in the housing. In the vacuum pump which is completely filled with liquid, there is the danger that when the vacuum is too great, the small amount of necessary lubrication liquid in the interior of the housing of the hose pump will foam, so that the restoring forces for raising the hose again cannot be generated or can only be generated to a reduced extent.